1. Field of the Invention
The present invention relates to a fuel cell.
2. Description of the Related Art
A solid polymer electrolyte fuel cell includes unit cells. Each of the unit cells includes a membrane electrode assembly (MEA) and a pair of separators sandwiching the MEA therebetween. The MEA includes an electrolyte membrane, which is a polymer ion-exchange membrane, and an anode electrode and a cathode electrode sandwiching the electrolyte membrane therebetween. The solid polymer electrolyte fuel cell, which usually includes a certain number of the unit cells that are stacked, is used as a fuel cell stack for an automobile.
In the above fuel cell, a fuel gas channel for supplying a fuel gas to the anode electrode is formed on a surface of one of the separators, and an oxidant gas channel for supplying an oxidant gas to the cathode electrode is formed on a surface of the other of the separators. Moreover, a coolant channel, through which coolant flows, extends along surfaces of the separators of the unit cells that are adjacent to each other.
Some fuel cells have an internal manifold structure. The internal manifold structure is built up of a fuel gas inlet manifold, a fuel gas outlet manifold, an oxidant gas inlet manifold, an oxidant gas outlet manifold, a coolant inlet manifold, and a coolant outlet manifold. These manifolds are disposed in the fuel cell and extend through the fuel cell in the stacking direction of the separators.
Such an internal manifold fuel cell has a problem in that it is difficult to uniformly supply a fuel gas and a oxidant gas (reactant gas) to a power generation section (power generation surfaces of electrodes) and thereby the power generation performance may lowered. For example, a fuel cell described in Japanese Unexamined Patent Application Publication No. 6-267559 addresses this problem.
This fuel cell includes a separator 1 illustrated in FIG. 10. Gas is supplied to the separator 1, and the gas flows through a gas inlet 2, a power generation section inlet 3, a power generation section, a power generation section outlet 4, and a gas outlet 5. A gas channel 6 extends from the gas inlet 2 to the power generation section inlet 3. Trapezoidal fin groups 7a, 7b, and 7c are disposed in the gas channel 6.
Each of the trapezoidal fin groups 7a, 7b, and 7c includes a large number of trapezoidal fins that are arranged in a staggered manner, and the trapezoidal fins are selectively oriented. That publication states that the pressure of the gas is substantially equalized in the power generation section inlet 3 due to the trapezoidal fins, and thereby the flow rate of gas in the power generation section inlet 3 is substantially uniform.
However, the fuel cell described in Japanese Unexamined Patent Application Publication No. 6-267559 has the following problems. First, the structure is complex and is not cost efficient, because the gas channel 6 includes the trapezoidal fin groups 7a, 7b, and 7c, each including a large number of trapezoidal fins that are arranged in a staggered manner and are selectively oriented. Second, a pressure drop of the gas is large, because the gas flows through the trapezoidal fin groups 7a, 7b, and 7c before being supplied to the power generation section through the power generation section inlet 3.
Third, a stack of the fuel cells becomes large, because, in order to uniformly distribute the gas, it is necessary that the gas channel 6 have a large size and thereby the proportion of the area of an electrode to the area of the separator (area utilization) is decreased.